There are already known electromechanical processes for metering electrical energy which are employed in the electricity meters of millions of subscribers to the public electricity service.
However, these electromechanical processes which have shown substantial proof of efficiency and reliability have the disadvantage that they require costly and bulky devices.
Furthermore, there are known processes for measuring electrical power which make use of techniques involving the separate measurement of the current and voltage, for example in a single-phase installation. In some of these known processes, the instantaneous voltage and current, after being measured and put into the appropriate shape, are multiplied by analog means.
The voltage taken directly from the installation or from the secondary winding of an isolating transformer is usually reduced so as to reach a signal level compatible with the input levels of an integrated multiplier circuit. The current can be measured either by means of a shunt, this being the most common technique, or by using a current transformer or employing a Hall-effect sensor.
In the first two cases, namely a shunt or a transformer, the main handicap is the bulk and weight of the installation. The use of a Hall-effect sensor adopting the known flux compensation technique solves any problem of galvanic isolation, especially difficult when a shunt is used, but is truly justified only in uses where an acquisition speed below a microsecond is necessary, because it has the disadvantage of employing devices which are complex and costly and which supply low-level output voltages.
Some of the processes for measuring power and energy employing the abovementioned measuring techniques make use, furthermore, of a digitization of the respective analog voltage and current signals, thus allowing a digital processing of the corresponding information. However, these processes, although of higher performance as regards the processing than the purely analog processes, nevertheless involve devices which are at least as costly and bulky because of the sensors, especially current sensors, used.